As a projector that projects color video images, there is known a projector with a field sequential type (also referred to as a single plate type) configuration in which a white light output from a light source is sequentially separated into three primary color lights of red, green and blue by means of a color wheel that rotates at a high speed, and forms a color video image by optically modulating each separated color light in accordance with a video image signal. A liquid crystal panel, a DMD (Digital Micro-mirror Device: a registered trademark), or the like is used as a video image formation device used for light modulation.
In the above-described projector using the color wheel, a high-luminance discharge lamp, or the like is used as a light source in the conventional mainstream configuration. However, in recent years, a projector using a semiconductor device such as a laser diode or an LED (Light Emitting Diode) as a light source is developed to increase the lifetime of the light source, reduce power consumption, and the like.
For example, Patent Document 1 (JP2014-139689A) discloses a projector using an LED or a laser diode as a light source, the LED or the laser diode emitting an ultraviolet light and a blue light. Patent Document 2 (JP2012-212129A) discloses a projector using a laser diode as a light source, the laser diode emitting a blue light.
When an LED or a laser diode is used as a light source, the LED or the laser diode generally outputs only a single wavelength light. In the projector disclosed in Patent Documents 1 or 2, a light output from the light source is irradiated as excitation light on phosphors to obtain three primary color lights of red, green and blue, so that the color lights that cannot be obtained from the light source directly are emitted from the phosphors, respectively. When a laser diode that emits a blue laser light is used as the light source, for example, a red light and a green light are emitted from the phosphors. Since luminous efficiency of the phosphor varies depending on the color light to be emitted (the type of phosphor), Patent Document 1 proposes that the projector be provided with two or more types of light sources that output lights of different wavelengths, to switch the light sources for emitting the excitation light depending on the phosphor.
The effect that is caused by the difference in the luminous efficiency of the phosphor can be reduced by reducing the types of phosphors. When the red light and the green light are emitted using the blue laser light as the excitation light, for example, the thinking is that it is better to use a phosphor that emits yellow light that includes red and green components rather than to use individual phosphors that emit red and preen right. In this case, the yellow light is preferably separated into the red light and the green light using the color wheel. Hereinafter, an apparatus that is provided with a light source, a phosphor, and the like, and outputs each color light for forming a color video image on a video image formation device that is referred to as a light source apparatus.
Thus, the projector in which the laser diode that emits the blue laser light is provided in the light source apparatus can obtain blue light with higher color purity and chroma than the projector in which the discharge lamp or the like is provided in the light source apparatus.
However, when each color light having the same level of luminance as the light emitted from the light source apparatus provided with the discharge lamp or the like is output from the light source apparatus provided with the laser diode, the blue light has the same luminance as that of the red light and the green light, but looks brighter than the red light and the green light. This is caused by the high chroma of the blue light obtained from the laser light, which is known as the Helmholtz-Kohlrausch effect (H-K effect).
Accordingly, when the blue laser light is used for the light source, chrome differences between the blue light and the red light and between the blue light and the green light become larger, and color breaking occurs in a projection video image more significantly than in a projector in which the discharge lamp or the like is used as the light source.